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United States Patent |
5,065,768
|
Coleman
,   et al.
|
November 19, 1991
|
Self-sealing fluid conduit and collection device
Abstract
A self-sealing fluid collection tube is provided with an elongated bore and
a fluid entry end. A plug of super-absorbent material is provided within
the tube opposite the fluid entry end. This plug is preferably vented and
is adapted to seal the tube by expanding when contacted by a fluid, such
as blood. After the fluid has been collected, the tube is placed in a
pipetter-dispenser in which a plunger, which is inserted into the tube,
moves through a calibrated distance thereby advancing the plug into the
tube and expelling a selected volume of fluid from the tube.
Alternatively, the fluid may be transferred into another receptacle by
piercing the sealed plug to form a new vent channel to permit drainage of
the collected fluid into a receptacle.
Inventors:
|
Coleman; Charles M. (Pittsburgh, PA);
Kendrick, Sr.; William G. (Doylestown, PA)
|
Assignee:
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Safe-Tec Clinical Products, Inc. (Ivyland, PA)
|
Appl. No.:
|
243982 |
Filed:
|
September 13, 1988 |
Current U.S. Class: |
600/573; 73/864.02; 422/916 |
Intern'l Class: |
A61B 005/00 |
Field of Search: |
128/760,763,765,766,770
73/864.02,864.03
604/15,21,51,52,126,134-136,187,90,218,226
279/41 R
|
References Cited
U.S. Patent Documents
3238941 | Mar., 1966 | Klein et al. | 604/218.
|
3480014 | Nov., 1969 | Callahan | 604/51.
|
3741732 | Jun., 1973 | Stanfield | 73/425.
|
3750667 | Aug., 1973 | Pshenichug et al. | 604/117.
|
3783696 | Jan., 1974 | Coleman | 73/425.
|
3864979 | Feb., 1975 | Ayres | 73/864.
|
3891392 | Jun., 1975 | Betts et al. | 73/864.
|
3952599 | Apr., 1976 | Ayers | 73/425.
|
3960139 | Jun., 1976 | Bailey | 128/2.
|
3995496 | Dec., 1976 | Bickford | 73/864.
|
4027660 | Jun., 1977 | Wardlaw et al. | 73/425.
|
4082085 | Apr., 1978 | Wardlaw et al. | 73/425.
|
4122947 | Oct., 1978 | Falla | 128/760.
|
4133304 | Jan., 1979 | Bailey | 128/2.
|
4137755 | Feb., 1979 | Wardlaw et al. | 73/61.
|
4159896 | Jul., 1979 | Levine et al. | 23/230.
|
4190328 | Feb., 1980 | Levine et al. | 350/320.
|
4267729 | May., 1981 | Eddleman et al. | 73/864.
|
4657454 | Apr., 1987 | Migita et al. | 279/41.
|
4781683 | Nov., 1988 | Wozniak et al. | 604/110.
|
Foreign Patent Documents |
0067726 | Dec., 1982 | EP | 128/760.
|
0166574 | Jan., 1986 | EP.
| |
0176080 | Apr., 1986 | EP.
| |
2176711 | Jan., 1987 | GB.
| |
Other References
"Quantitative Buffy Coat Analysis, A New Laboratory Tool Functioning as a
Screening Complete Blood Cell Count", by Wardlaw and Levine, 1983.
Chemical Abstract 105: 80370h, Feb. 1986.
Chemical Abstract 105: 99323d, Feb. 1986.
Chemical Abstract 105: 135280y, Oct. 1984.
Chemical Abstract 105: 6575v, Jul. 1986.
Article "Simikagel SP-520 High Absorptivity Polymer", Nov. 1984.
Brochure "Aridall 1080 Superabsorbent Polymer", Mar. 1987.
Fisher Scientific Catalog 1986, pp. 407, 409.
Lancer Laboratory Supplies Catalog, 1981, by Sherwood Medical.
|
Primary Examiner: Hindenburg; Max
Attorney, Agent or Firm: Buchanan Ingersoll
Claims
We claim:
1. A self-sealing tube comprising a tubular body having an elongated bore
and a fluid entry end, and a movable plug of super-absorbent containing
composite material provided within said tube, said super-absorbent
material adapted to expand when contacted by an aqueous fluid and seal
said tube to prevent passage of air and liquids through the plug during
centrifugation and expulsion.
2. The tube of claim 1 wherein said plug has an opening provided therein,
said opening sized to vent said tube when fluid enters said tube, said
opening being closed by the expansion of said plug of super-absorbent
material when contacted by said aqueous fluid.
3. The tube of claim 2 wherein said super-absorbent material comprises a
super-absorbent polymer and an organic support matrix.
4. The tube of claim 3 wherein said super-absorbent polymer is an acrylic
acid containing polymer.
5. The tube of claim 4 wherein said organic support matrix is a member of a
class consisting of organic polymers, fats, waxes and thixotropic oils
blended into a composite material.
6. The tube of claim 1 wherein said plug of super-absorbent material has a
specific gravity greater than the heaviest component of the fluid.
7. The tube of claim 6 wherein said super-absorbent material comprises a
super-absorbent polymer and an organic support matrix.
8. A self-sealing blood and body fluid collection tube for capillary
collection of blood and other body fluids comprising a unitary tubular
body having an elongated bore and a fluid entry end, and a super-absorbent
containing composite material comprising a super-absorbent polymer and an
organic support matrix provided within said tube opposite said fluid entry
end, said super-absorbent material adapted to expand when contacted by one
of blood and a body fluid and seal said tube to prevent passage of air and
liquid through the plug during centrifugation and expulsion.
9. A self-sealing movable plug for use in a fluid collection tube, said
plug provided with a vent channel extending therethrough, said plug being
comprised of a super-absorbent containing composite material that will
swell to seal said tube and be impermeable during centrifugation and
expulsion to air and to liquids after said fluid contacts said vent
channel of said plug.
10. The self-sealing plug of claim 9 wherein said plug comprises a
super-absorbent material adapted to expand when contacted by said fluid.
11. The self-sealing plug of claim 10 wherein said super-absorbent material
comprises a super-absorbent polymer and an organic support matrix.
12. The self-sealing plug of claim 11 wherein said super-absorbent polymer
is an acrylic acid containing polymer.
13. The self-sealing plug of claim 11 wherein said organic support matrix
is a member of the class consisting of organic polymers, fats, waxes, and
thixotropic oils blended into a composite material.
14. The self-sealing plug of claim 9 wherein said plug comprises an acrylic
acid polymer dispersed within a support polymeric organic support matrix.
15. The self-sealing plug of claim 9 wherein said fluid is a fluid
containing at least two components having a different specific gravity and
said plug has a specific gravity greater than the heaviest component of
the fluid.
16. The self-sealing plug of claim 9 wherein said fluid is blood.
17. A system for the collection, separation and dispensation of an aqueous
fluid containing at least two components having a different specific
gravity comprising:
(a) a unitary tubular body having an elongated bore and a fluid entry end,
a plug of super-absorbent material provided within said tube opposite said
fluid entry end, said plug having a specific gravity greater than the
component of the fluid having the highest specific gravity, and at least
one sealant material provided within said tube, said sealant material
having a specific gravity intermediate that of at least two of the
components of the fluid; and
(b) dispensing means adapted to receive said fluid collection tube after
the components of said fluid and sealant material within said tube have
been separated, said dispensing means comprising:
(i) a housing adapted to receive said tube;
(ii) a rod member extending axially through said housing, said rod member
sized to fit into said fluid collection tube;
(iii) an adjustment means connected to said rod member and said housing to
permit movement of the rod member relative to the housing;
(iv) a plunger member connected to an end of said rod member, said plunger
member extending outward from said housing; and
(v) adjustable stop means provided on said plunger member, said stop means
capable of being positioned at any desired one position of several
positions on said plunger and adapted to permit said plunger to travel a
calibrated distance into said housing, said calibrated distance being
directly related to said desired one position of the stop means on said
plunger.
18. The system in claim 17 wherein the fluid collection tube has a fluid
collection chamber of a known volume and the dispensing means is adapted
to expel a pre-determined volume of separated fluid.
19. The system of claim 18 also comprising a hydrophobic coating applied to
the inner diameter of one end of said collection tube.
20. The system of claim 18, wherein said collection tube is a capillary
tube having one end thereof flared outward.
21. The system of claim 18 wherein said dispensing means further comprises:
(a) a housing;
(b) a rod member extending axially through said housing, said rod member
sized to fit into said fluid collection tube; and
(c) an adjustment means connected to said rod member and said housing to
permit movement of the rod member relative to the housing.
22. The system of claim 21 wherein said adjustment means comprises:
(a) a plunger member connected to an end of said rod member opposite said
plug means, said plunger member extending outward from said housing;
(b) stop means provided on said plunger member, said stop means adapted to
permit said plunger member to travel a calibrated distance into said
housing; and
(c) return means engaged on said plunger member, said return means adapted
to fully extend plunger a calibrated distance out of said housing.
23. The system in claim 22 wherein said return means is a spring.
24. The system of claim 21 also comprising a plug attached to said rod
member, said plug sized to fit into the fluid collection tube.
25. The system in claim 21 wherein said dispensing means further comprises
a locking means which secures said collection tube within said housing.
26. The system in claim 17 further comprising identification means provided
on said collection tube.
27. The system in claim 26 in which said identification means is at least
one of a label applied on said collection tube and a label applied on a
cap adapted to cover said collection tube.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for the handling
and control of fluids in conduits, particularly small bore tubes, with new
and novel plugs adapted to seal on contact with the fluid. More
specifically, the present invention relates to the collection of aqueous
fluids, such as blood, in small bore tubes. Additionally, the present
invention relates to a conduit which will automatically seal itself after
collection of the fluid, to a dispenser-pipetter which cooperates with the
plug to dispense precise micro-volumes of a fluid from the collection
tube, and to a small bore collection tube fitted with a venting puncture
cap that permits transfer drainage of the contents of the collected
specimen into a receptacle.
2. Description of the Prior Art
It is well known in the art to collect and centrifuge fluids, such as
blood, in small bore or capillary tubes in order to determine the fraction
of the cellular constituents relative to the total volume of blood. This
is known as the packed cell volume or the hematocrit. In the Approved
Standard of the National Committee For Clinical Laboratory Standards
(NCCLS) known as the "Microhematocrit Method", capillary blood collection
tubes are sealed immediately after collection of the blood. Generally, the
tubes are sealed by pressing the thin capillary tube into a layer of
clay-like sealing compound provided in small trays, five to seven
millimeters in depth. Subsequently, the tubes are centrifuged and the
ratio of the height of the red blood cells to the total height of the
blood column, which includes all the cells (red and white) plus the light
phase, also called the serum or plasma, is determined. This ratio,
expressed as a percentage, is called the hematocrit value, and decimally,
as the packed cell volume.
This procedure to obtain the hematocrit value by the widely used Approved
Standard Microhematocrit Method provides a significant health risk to the
laboratory worker or other medical personnel conducting the test. The
capillary collection tubes are specified by the NCCLS to be within certain
tolerances. Current specifications require a tube seventy-five millimeters
in length, 1.155 millimeters in internal diameter, and the wall 0.2
millimeters thick. Present tubes are made of glass and are readily
breakable. Glass tubes have broken when a technician presses the tube into
a sealing compound. If a tube breaks, broken glass may penetrate the
finger of the laboratory worker, thereby inoculating the blood within the
tube into the worker. If this happens, the worker is at high risk of
infection with viruses or whatever infectious units are present in the
collected blood. Thus, there is a need for an integrated capillary
collection tube that eliminates the hazardous step of pressing the device
into a sealant after the blood is collected.
We have found that it is possible to collect skin puncture blood specimens
directly into narrow bore (0.5-0.6 mm) capillary tubes, such as Becton,
Dickinson's Pre-Cal Micro-Hematocrit Tubes providing that they are plugged
with the conventional clay-like sealing compound recommended by the NCCLS,
if a vent channel of about 0.2 mm diameter is present, and if
extraordinary precautions are made to maintain the collection tube
horizontal from the initial collection stage, through the placement of the
tube within a Microhematocrit Centrifuge that has been specially fitted
with a soft rubber padding band directly inside the standard base band for
the capillary tubes. It is noted that this extraordinary procedure
requires special care and meticulous handling, and that there is no margin
for error. The consequences of failure are loss of blood from the inside
of the tube, with contamination of the environment. It is a very hazardous
procedure, with nothing to recommend it as it stands.
It has also been the practice in the past that, when processing small
volumes of centrifuged blood for chemical or serological testing,
technicians have removed serum or plasma from the collection vessel and
manually measured the amount desired using a pipet or a
pipetter-dispenser. This requires the use of two vessels: the collection
vessel and the dispensing vessel. An integration of these vessels would
result in economy of operator time and materials. By reducing exposure to
the blood, such a device would reduce the risk of blood-borne infections.
Therefore, there is a need for a single vessel which combines the
operations of collection, separation, and micro-volumetric dispensation of
blood.
It is further known that certain water absorbing polymers that are
covalently cross-linked or possess ionic interaction between polymer
chains, designated "super-absorbents", have high water absorbancy
characteristics which cause them to expand greatly, forming gel particles
in the presence of water. These are designated by some as hydro-gel. These
products are used widely to absorb water from body fluids and have been
incorporated in personal hygiene products such as infant's diapers and
women's sanitary products. They are also used as water-retaining materials
for agricultural mulches. In a finely divided form and combined with
rubber or elastomers, these super-absorbents have been used in
well-drilling operations to stop leaks in pipes, and with rubber,
elastomers and/or other organic resins to make water swelling paints,
pastes, gaskets, coatings of electrical wires, and other products having
unique water-swelling and water-retaining properties. Super-absorbent
composite materials have been developed which can expand by water
imbibition more than 25 times their original volume, depending on
conditions. Composites of super-absorbent polymers with resins and
elastomers are formulated to provide greatly enhanced strength and other
physical properties which the super-absorbent's weak hydrated gel
structure does not possess when used alone.
SUMMARY OF THE INVENTION
The present invention comprises an apparatus and method for the collection
of fluid with the option of separation and/or dispensation. The apparatus
includes a collection tube and, optionally, a pipetter-dispenser, or a
specimen transfer tube, consisting of a collection tube fitted with a vent
channel puncture means to permit air reentry into the tube and subsequent
fluid drainage of the collection tube. The collection tube includes a
self-sealing fluid collection tube having a unitary tubular body, which
preferably is either a glass or organic polymer. The tubular body is
provided with an elongated bore and a fluid entry end. A super-absorbent
plug composed of a of water-swellable material is provided within the tube
opposite the fluid entry end. This plug is adapted to imbibe water and
swell (expand) when contacted by an aqueous fluid and seal the tube. A
vent channel is provided within the plug to allow air within the tube to
escape when fluid enters. Expansion of the plug causes the vent channel to
constrict, thereby blocking any further venting and stopping flow of fluid
into the tube.
The present invention is ideally suited for the microcollection of body
fluids, especially blood, in capillary and other small bore tubes. It is
particularly useful for blood obtained by means of a skin puncture. If the
collection tube is intended to have its contents separated by
centrifugation, the plug, which is generally formed from a composite,
should have a specific gravity greater than that of the blood cells. If
the plug is comprised of a material which bonds or strongly adheres to the
tube wall, the specific gravity of the plug may not be important. Upon
centrifugation, the plug is deformed under compression, thereby improving
the seal resulting from the swelling of the plug caused by the contact
with the blood.
We have found that various organic polymers and materials, such as beeswax,
organic oils such as silicones, hydrocarbons, esters, and the like,
rendered thixotropic by addition of finely dispersed agents, such as
amorphous silica gel and solid fats, can serve as organic matrices for the
super-absorbent polymers. For blood collection tubes, the specific gravity
of these materials should be generally greater than about 1.09 (the
density of the blood cells, the heaviest component of the blood) and the
material should have sufficient compliance to compress and form a seal at
a level of centrifugal force generally adequate to determine the packed
cell volume. We have found that the best results are obtained using a
mixture of a finely divided cross-linked acrylic acid polymer within a
support polymer matrix. In a preferred embodiment, a co-polymer of acrylic
acid and vinyl alcohol is mixed into a rubber matrix. The polymer
preferably is about 60 microns or less in diameter and cross-linked. Other
super-absorbent materials composed of acrylic acid such as the
homopolymers of acrylic acid are also effective when reduced to about 20
to 40 microns mean diameter. Moreover, super absorbents, such as
starch-acrylic acid graft polymers and acrylic acid block co-polymers also
may be used when dispensed within a support matrix.
A gel separator element, such as that used in a vacuum blood collection
tube for the collection and separation of venous blood, may be placed
within our capillary tube having a self-sealing plug at one end. The gel
is preferably in the form of a short rod segment and is provided along one
side of the tube wall. Alternatively, a ring of gel may be provided near
or in contact with the self sealing plug. The separator gel has a specific
gravity intermediate the light phase and heavy phase of the blood. Upon
centrifugation, the gel proceeds to the interface of the light and the
heavy phases of the blood to form a seal therebetween. This embodiment is
used when it is desired to maintain the light and heavy phases of the
blood isolated from each other for an extended period of time.
If one desires to use our tube for storing blood, he may want to reduce the
imbibition of water into the plug from the blood after centrifugation.
This can be done by adding to the tube a grease or other material having a
specific gravity between the specific gravities of the plug and the blood.
When blood enters the tube it will contact the plug to make it swell and
seal. After centrifugation the added material will form a barrier between
the blood and the plug thereby blocking water flow from the blood into the
plug.
The collection tube may be used in a specimen transfer mode without
centrifugal separation if a vent channel puncture means is incorporated
into the collection device. A simple integrated device would add a cap at
the end of the tube and closely adjacent to the sealed self-sealing plug.
The tube will hold the aqueous specimen in the tube by air pressure when
the specimen is collected, the fluid contacts the vent channel, and the
plug thereupon sealed. When it is desired to transfer an unseparated
specimen, such as is the case with micro-specimens for blood gas analysis,
a hypodermic needle, or a small bore molded cannula with sharper point is
pressed through the plug to permit air flow to proceed through the sealed
plug, and allow transfer of the collected fluid out of the collection
tube, and into the receptacle. Preferably, this needle is incorporated
into a cap which fits over the plugged end of the tube. This is the
simplest way to dispense collected specimens, but not the most precise.
Preferably, a pipetter-dispenser is used to dispense a measured quantity of
collected fluid. The pipetter-dispenser has a housing having a thin rod
member extending axially therethrough. The rod member is adapted to fit
within a collection tube. One end of the rod member is attached to a
plunger which extends out of one end of the housing. Stop means are
provided on the plunger to permit the plunger to travel through a
calibrated distance. The opposite end of the housing is provided with a
collet which locks the capillary tube in place within the elongated body.
We have found that it is preferable, but not essential, for the
collection-separation-dispensation mode tube to have a slight flare at the
end nearer the plug. In use, the flared end of a precision bore capillary
tube is inserted into the pipetter-dispenser in such a way that the rod
member extends into the tube and abuts the plug. The rod member should
push against the super-absorbent plug until the fluid is at the end of the
tube or at another selected position within the tube. At this point, the
tube is locked in place by means of the collet. As the plunger is
depressed, the rod member extends further into the capillary tube and
pushes against the plug located at the end of the capillary tube. Because
the distance the plunger travels has been calibrated, a known and precise
amount of fluid is expelled. If the plug is intended to be moved by a
dispenser, the plug should not bond to the tube wall. Bonding can be
prevented by appropriate selection of materials for the plug, or use of a
release agent on the inner wall of the tube.
The capillary tubes used with the pipetter-dispenser can be formed from
molded or extruded synthetic resins or elastomers. Alternatively, the
tubes can be opaque tubes formed from metal or ceramic materials.
Moreover, the tubes can be formed from the glass which is specified by the
American Society for Testing Materials (ASTM) as the standard for
capillary tubes used in the NCCLS Microhematocrit Method. Finally, a glass
capillary tube that is covered by a polymer protective film or tubular
sheath can be used. Such film or tubular sheath, if clear, would enable
the contents of the tube to be visually or photo-optically examined, while
protecting the user from injury that might occur upon handling and
centrifugation of the tube. Such a sheath can be used to provide even
further protection for the user from accidental injury from glass
particles that might be released upon centrifugation.
With the use of the new and novel self-sealing plug in collection tubes
intended to handle biological specimens there are several options of usage
combinations. First, the plug can be used to form a self-sealing
microhematocrit tube for the collection and centrifugal separation of
blood. This provides an apparatus for a simplified and safe determination
of the packed cell volume. Second, the plug can be used to form a tube
which provides for the integration of the collection, separation, and
micro-volumetric dispensation of either blood plasma or blood serum.
Third, the self-sealing plug may be used in a tube simply to collect and
hold blood. A disposable Wintrobe Tube of this sort can be used to
determine the Erythrocyte Sedimentation Rate, wherein the self-sealing
plug is substituted for the usual cotton plug. Fourth, the self-sealing
plug used in the collection tube may be revented. In this mode, the tube
may be used as a transfer device i.e., both for the collection of the
specimen, and the subsequent drainage of the tube contents into a desired
receptacle. Such a situation occurs when micro quantities of blood are
collected for blood gas analysis. The collection tube may be fitted with a
cap holding a narrow gauge cannula, such as a 27 gauge hypodermic needle,
poised above and pointed toward the self-sealed plug. When it is desired
to release the contents of the tube (which may be held "upside down"
within the tube by air pressure in conjunction with surface tension), into
the desired receptacle, the cap is pressed, the hollow needle penetrates
the plug, the air pressure supporting the fluid is nullified by air
entering at the opposite end and the specimen drains from the collection
tube into the receptacle as a consequence of the gravitational force
causing outward flow. Several blood gas analysis apparatus instruments can
use this type of tube. Finally, the self-sealing plug may be used in a
capillary tube for the collection of aqueous fluids followed by direct
dispensation of the unseparated fluid. Such may be desired for
micro-volumetric dispensation of capillary collected blood into
hematological counters, or onto dry strips that use whole blood. Urine may
also be handled in this manner, wherein it is collected and then
dispensed, without separation by use of a pipetter-dispenser or vent tube
penetration of the sealed plug.
A BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an fragmentary isometric view of a first present preferred
embodiment of the fluid collection tube of the present invention.
FIG. 2 is a cross-sectional view of the fluid collection tube of FIG. 1
taken along the line II--II.
FIG. 3 is a sectional view of a third present preferred embodiment of the
fluid collection, separation, and dispensation tube of the present
invention.
FIG. 4 is a sectional view of the fluid collection tube of FIG. 3 after
collection and centrifugation of a non-homogeneous fluid.
FIG. 5 is an perspective view partly in section of the pipetter-dispenser
of a preferred embodiment of the present invention.
FIG. 6 is a partial perspective view partly in section showing the
capillary tube of FIG. 4, after it has undergone centrifugation, inserted
into the pipetter-dispenser of FIG. 5 for operation.
FIG. 7 is an elevational view of our collection tube fitted with a
reventing cap to form a transfer tube.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A system for the collection, separation and dispensation of a fluid is
provided which includes fluid collection tube 10 and pipetter-dispenser
50. As shown in FIGS. 1 and 2, fluid collection tube 10 is preferably
provided with plug-end 12 and opposite end 14. The fluid to be collected
enters tube 10 through opposite end 14. Preferably, tube 10 is in the form
of a capillary tube. However, tubes 10 of various sizes and shapes can be
used.
A plug 16 of super-absorbent material is provided at the end 12 of the
fluid collection tube 10. A vent channel 18 is provided axially within
plug 16 to provide an outlet for the gas displaced during fluid
collection. Alternatively, plug 16 may be formed so that a vent channel is
formed by a gap between plug 16 and the inner wall of tube 10. This vent
channel permits air displacement when the tube fills with a liquid. When
used in a capillary tube, vent hole 18 is necessary to permit air
displacement so that fluid may flow into tube 10. Alternatively, and
preferably when dispensation is intended, a slightly flared end 32 is
provided, as shown in FIGS. 3 and 4.
As the fluid enters tube 10 and reaches the end 12 of tube 10, it causes
the vent channel 18 provided in plug 16 of super-absorbent composite
material to imbibe, swell, and constrict. As the plug 16 swells, it
constricts and closes vent channel 18 and seals end 12. In this manner,
fluid collection tube 10 provides an efficient means to collect a fluid.
Fluid collection tube 10 is formed by inserting the plug 16 of
super-absorbent composite material into the end 12 of a standard capillary
tube 10. Alternatively, if hand micro-volumetric dispensation of fluid is
desired, a tube 30, as shown in FIGS. 4 and 5 having a length of 75 mm and
an inner diameter of 1.25 mm or greater is preferred so that a greater
volume of fluid could be used. We have found that the thickness of the
tube wall of a glass tube should be about 0.3 mm to accommodate the
pressure exerted against plug 36. Preferably, plugs 16 and 36 are
approximately 3.2 mm to 6.4 mm in length and substantially fill the inner
diameter of tubes 10 and 30. Vent channel 18 is provided through the plug
16 by inserting a thin wire therethrough. Preferably, vent channel 18 is
approximately 0.1 to 0.2 mm in diameter. Such a vent channel 18 would
provide a sufficient cross-sectional area for the displaced air to exit
the capillary tube 10. The vent channel 18 may be of any cross-sectional
shape although we prefer to use round and oval shapes.
Fluid collection tube 10 is ideally suited for the micro-collection of
blood in a capillary tube. Preferably, the super-absorbent composite
material in collection tube 10 has a specific gravity greater than that of
the heaviest component of the blood.
Alternatively a disposable capillary collection tube which is generally
recommended for the Microhematocrit Method by the NCCLS can be used as
tube 10. Such a tube, which should meet ASTM specifications is preferably
75 mm.+-.0.5 mm in length, has an internal diameter of 1.155.+-.0.085 mm
and has a wall thickness of 0.2 mm. This tube is composed of borosilicate
glass, type I, class B, or soda lime glass, type II, with specifications
on taper. However, tubes of various lengths, inside diameters, and
markings can be used.
Becton, Dickinson and Company markets a capillary tube for use in the
hematocrit determination that is provided with an inside diameter of
smaller diameter than the ASTM standard capillary tube. This tube has a
thicker wall and is marked to fill a blood column 60 mm in length. These
tubes may be fitted with the self-sealing plugs of this invention. The
plugs of this invention can also be used with tubes that handle other
aqueous fluids. Such tubes are extruded or molded from organic polymers
and are preferably provided with a hydrophilic surface. In addition, the
plugs of this invention may be used with tubes that are coated with a
polymer film jacket or which have a shrinkable tubing placed over the
glass capillary tube.
The Disposable capillary tube operates in a similar manner to fluid
collection tube 10. A plug of super-absorbent material is provided at one
end of the tube. The fluid to be collected enters the tube through the
opposite end. A vent channel is provided within the tube to provide an
outlet for the gas displaced by the collected fluid.
A variety of compounds can be used as the super-absorbent. A
super-absorbent polymer mixed with an organic carrier material or matrix
provides the appropriate swelling characteristics and strength required
for the plug. A mixture of rubber and acrylic acid, such as a cross-linked
acrylic acid or an acrylic acid grafted onto starch or copolymers of
acrylic acid/vinyl alcohol cross-linked, or acrylic acid containing block
co-polymers perform well in sealing the collection tubes under most
circumstances. In the preferred embodiment next described, such a
composition is capable of swelling 25 or more times its original size in
distilled water and 8 or more times in blood.
Present preferred embodiments of our composite containing a super-absorbent
polymer are set forth in the following examples.
EXAMPLE I
Five grams of Dow-Corning "100% Silicone Rubber General Purpose Sealant,
Clear", obtainable from hardware stores, was mixed with five grams of
Sumikagel SP520 supplied by the Sumitomo Chemical Company of Tokyo, Japan,
and the two ingredients were thoroughly blended to yield a soft,
putty-like composite material in which the Sumikagel SP520, an
acrylic/vinyl co-polymer, sodium salt, about 20 to 30 microns in size, was
dispersed throughout the room temperature vulcanizing silicone rubber
matrix. Capillary tubes, both of the type used for the Microhematocrit
Method, and precision bore tubes for use in collection, centrifugal
separation, and microvolumetric dispensation were found to be easily
plugged by the same simple method as used in sealing the tubes with the
clay-like sealant recommended in the NCCLS Microhematocrit Method. Soon
after a plug of 3.2 to 4.8 mm. in length was pressed into the tube, a wire
of 0.2 mm diameter was forced through the axial part of the plug, and
withdrawn. The tubes were then set aside to cure over a period of three
days at 20.degree. to 23.degree. C. When the self-sealing plug is made for
use with tubes intended for dispensation of centrifugally separated plasma
or unseparated biological fluids (as whole blood), a mold release agent is
desirable. General Electric Silicone II Sealants were found to be equally
effective when purchased from retail hardware stores and properly blended
with acrylate super-absorbent polymers. Finely divided Aridall 1125, sold
by the Chemdal Corporation of Arlington Heights, Ill., has also been found
to be satisfactory when reduced in size to particles of 40 microns, or
less, and then blended with raw rubber stock and plasticizers. The Aridall
1125 is a cross-linked homopolymer of acrylic acid, potassium salt, and is
preferably blended to give a final concentration of about 50% by weight in
the ensuing elastomer composite. The specific gravity of the self-sealing
plug is preferably greater than the heaviest component (in blood, the red
blood cells) unless the rubber adheres tenaciously to the inner wall of
the tube. The material must be firm enough to maintain a vent channel. The
material must also be compounded so that a smooth plug is formed that is
in full contact with the wall of the tube. The procedures to be used in
mixing and blending the rubber or rubber-like material and the finely
divided super-absorbent materials, with additional processing aids and
compounding ingredients, such as plasticizers and pigments are well known
and commonly used by those skilled in the art of rubber compounding.
EXAMPLE II
A black composite is suitable for use in tubes 10 and 30. However when the
tube is used for blood collection there is less contrast between the plug
and the blood. The Oyo Corporation of Japan sells an aggregate mixture
called "Nistop", which is expressly intended to retain ground water from
entering bore holes drilled for oil and gas exploration. The aggregate
consists of black lumps and pieces, generally 3 mm and larger, dispersed
within granules of a super-absorbent polymer. The black lumps are a
composite comprised essentially of a finely divided acrylic acid polymer
dispersed within an elastomeric material and carbon black. The acrylic
acid polymer is Sumikagel SP520.
The black viscoelastic super-absorbent composite in the Nistop aggregate is
satisfactory for the fabrication of self-sealing plugs for the collection,
separation, and dispensation of microvolumes of the plasma phase of
collected blood. The black Nistop material can be used for the
determination of the packed cell volume, excepting that its dense
blackness makes poor contrast against the border of the dark red packed
blood cells. This make it difficult to distinguish the baseline (zero
value).
Other water-swellable rubbers, both vulcanized, and unvulcanized may be
used. We have found some compositions manufactured by Seitetsu Kagaku to
be acceptable. These were water-swellable rubber compounded with
styrene-butadiene rubber, and nitrile-butadiene rubber, unvulcanized,
containing Sumikagel SP520, and carbon black. Both were found to make
self-sealing plugs which were jet black, and to have self-sealing
functions.
Our self-sealing plugs may be formed in situ, as have the ones generally
described above in these specifications. They also may be made by
extrusion, and co-extrusion processes, and injection and other molding
procedures. The extruded tubing, with a vent channel must have sufficient
strength to hold its shape during the manufacturing, and intended
functions. Co-extruded tubing can be utilized for making plugs with the
proper strength, lubricity, and other properties needed for contact with
the tubular surfaces inside which the self-sealing plug is positioned.
This is especially true if the self-sealing plug is operating as a piston
is moved by a push rod. Those skilled in the art will recognize that there
are a multitude of ways in which the self-sealing plug may be
manufactured. The particular method selected will likely depend upon
equipment availability and other process factors.
Tubes may be used for collection and dispensation of fluid without the
intermediary operation of separation. After blood fills to the
self-sealing plug 16, it may be measured out micro-volumetrically with a
pipetter-dispenser into any diagnostic field such as a dry chemistry
strip, or into a measured volume of diluent for hematological testing.
A further embodiment of our collection tube can be seen in FIG. 3. In this
embodiment, fluid collection tube 30 has a fluid entry end located at
opposite end 34. Plug 36 of a super-absorbent containing composite
material is provided in the slightly flared end 32 of blood collection
tube 30. Vent channel 38 is provided through plug 36 to vent tube 30 to
permit capillary action. This vent channel will close when blood or
another fluid comes in contact with it. The super-absorbent composite
material used in plug 36 is selected so that the specific gravity of plug
36 is heavier than that of the heavy phase of blood. Interphase gel
sealant material 40 is provided alongside the inner wall of tube 30. Gel
sealant material 40 is chosen such that its specific gravity is
intermediate that of the light and heavy phase of the blood.
After blood has been introduced into fluid collection tube 30, tube 30 can
be centrifuged to separate the blood into its light and heavy phase
components. Centrifugation will cause interphase gel to move from the
sidewall to the position shown in FIG. 5. FIG. 4 shows tube 30 after it
has been centrifuged. After centrifugation, sealant 40 is located
intermediate the light phase 44 and heavy phase 46 of the blood. Plug 36
remains at slightly flared end 32 of tube 30, sealed, compacted, and
adjacent the heavy cellular phase 46 of blood. In this manner, tube 30 can
be used in the collection and sealed separation of the blood.
In order to dispense a measured volume of fluid from collection tube 10 or
30, we provide a dispenser 50 as shown in FIGS. 5 and 6.
Pipetter-dispenser 50 includes elongated body 52 through which thin rod
member 62 axially extends. Preferably plug 64 is provided at one end of
rod member 62. Alternatively, rod member 62 could be made large enough in
diameter so that plug 64 is not needed. The opposite end of rod member 62
is attached to plunger 54 which extends out of one end 58 of housing 52.
Stop means 56 is provided on plunger 54 and permits plunger 54 to travel
through a calibrated distance. Stop means 56 can be permanently attached
to plunger 54 or it can be in the form of a set screw which can be
positioned along plunger 54 and calibrated according to scale 55. A
locking collet 66 is provided on the end of housing 52 opposite end 58 and
is adapted to lock capillary tube 10 within pipetter-dispenser 50.
When knob 68 is depressed, plunger 54 is forced into housing 52. The
abutment of stop means 56 against end 58 of housing 52 causes plunger 54
to stop its descent. Because the distance "D" between extended stop means
56 and end 58 has been calibrated, plunger 54 moves a known distance when
fully depressed. Spring 60 acts on plunger 54 to force plunger 54 back out
of housing 52.
In use slightly flared end 32 of capillary tube 30 is inserted into
pipetter-dispenser 50 such that rod member 62 can extend into the tube 30.
Tube 30 is then pushed into pipetter-dispenser 50 until the serum or
plasma component of the blood is at the end 34 of the tube or at
calibration line 17. Thereupon, tube 30 is locked in place by turning
collet 66. As plunger 54 is depressed, rod member 62 extends further into
capillary tube 30 and plug 64 pushes against plug 16 located within the
capillary tube, thereby expelling blood serum or plasma. Because the
distance which plunger 54 travels has been calibrated, a known and precise
amount of fluid is expelled.
An added advantage of our invention is that identical multiple samples of
blood plasma or serum can be obtained when the tube 30 has a constant
inner diameter. After each depression of plunger 54, tube 30 is positioned
within housing 52 in accordance with the procedure set forth above.
Limited only by the amount of serum or plasma remaining in tube 30,
plunger 54 can be depressed a number of times to produce a number of
samples having identical quantities of blood or serum therein.
Consequently, a number of different tests can be performed on the blood
collected in a single capillary tube.
Although our invention has been described in relation to its use for
precise measurement, our pipetter-dispenser 50 can be used as an ordinary
fluid dispenser. Even if a tube 30 having an irregular inner diameter is
used to collect the fluid, the dispenser 50 will nevertheless expel a
volume of fluid. Such a use of our invention is appropriate where exact
volumes of fluid to be tested are not required.
It should be obvious that this invention may also be used for the two steps
of collection and dispensation of micro-volumes of unseparated fluid, such
as whole blood in those circumstances where minimal contact of the blood
is required, yet an accurate dispensation of whole blood is needed. This
requirement prevails in hematological studies where electrochemical
counting of diluted whole blood, and other studies are made. The
self-sealing plug permits collection in a self-sealing tube, with the rod
propulsion of the plug. Some analytical systems, especially with the use
of dry chemistry testing strips, utilize whole blood, yet need a
moderately precise micro-volume of blood dispensed onto the strip.
In those cases where it is desired to collect and transfer whole blood for
certain uses, such as blood gas determinations and where it is not desired
to either separate the blood, or unnecessary to pipet exact volumes of
blood, the addition of a reventing cap to a collection tube with
self-sealing plug permits the collection and transfer of the collected
specimen by drainage of the collected column of fluid by gravity. The
penetration and reventing of the sealed plug counterbalances the air
pressure, i.e, the vacuum hold on the fluid column is broken and the
specimen flows into a receptacle. In the case of a micro blood gas
specimen, the capillary tube filled with blood for a blood gas
determination is connected with a reception tube input of a micro blood
gas analysis machine.
FIG. 7 shows micro blood gas tube (transfer tube) 70 sealed and filled with
heparinized blood. A reventing cap 72 is slidingly provided adjacent the
sealed self-sealing plug 76. Closure cap 74 is fitted at the blood entry
end. The tube is revented by sliding reventing cap 72 inward along tube 70
thereby piercing the self-sealing plug 76 with 27 gauge hypodermic needle
78 attached to reventing cap 72. Needle 72 is preferably 13 mm in length.
Identification means can be added to the capillary tube 10 of this
invention to provide safeguards against misdiagnosis of a patient's
condition. The identification means can consist of a label provided
directly on tube 10 or on a cover cap which is adapted to fit over end 14
of the tube 10. Further protection is obtained by using both of these
identification means. Proper use of the identification means prevents a
sample from one patient being confused with that of another, thereby
preventing a misdiagnosis from occurring by testing of his labeled sample.
In this specification, we have used blood as an example of the type of a
fluid to be tested which can be collected within small bore tubes.
However, it is to be understood that the present invention relates to any
aqueous fluid which can be collected and tested. Also, in this
specification we have used a capillary collection tube as an example of a
vessel which can collect fluid. It is to be understood that the present
invention relates to and can be adapted for use with any vented tubular
device or a device having a tubular portion which can collect, separate,
dispense or transmit fluids. Such containers include capillary blood
collection tubes, micro-hematocrit capillary tubes, Caraway capillary
tubes, urine sediment tubes, small bore tubes, blood gas determination
tubes, capillary tubes, capillary tubes for blood collection, blood
chemistry determination tubes, Wintrobe sedimentation pipets and Natelson
capillary tubes, and preloaded Quantitative Buffy Coat determination tubes
of Wardlaw, Levine and Massey, with interphase floats and fluorescent dyes
of the type sold by Becton, Dickinson and Company.
In addition, aqueous fluid that may be utilized in fluid transmission
tubes, which require certain safety check valves, can utilize the
self-sealing plug element of this invention where single use check valves
are required.
The collection tubes described above may also be used with anti-coagulants,
such as heparin (and its various cation salt derivatives), or with
clotting accelerators such as prothrombin. When plasma is dispensed,
specific agglutinating substances, such as antibodies or phytoagglutinins,
added by coating of the tube walls, to aid in holding the cells together
during dispensation, may be included in the device of this invention.
While we have described certain presently preferred embodiments of our
invention, it is to be distinctly understood that the invention is not
limited thereto and may be otherwise variously practiced within the scope
of the following claims.
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